This disclosure relates to voice removal techniques. Such techniques may be useful in a variety of applications, including the now very popular field of karaoke entertaining. In karaoke a (usually amateur) singer performs live in front of an audience with background music. One of the challenges of this activity is to come up with the background music (i.e. get rid of the original singer's voice to retain only the instruments so the amateur singer's voice can replace that of the original singer).
One way in which this can be achieved consists of using a stereo recording and making the assumption (usually true) that the voice is panned in the center (i.e., that the voice was recorded in mono and added to the left and right channels with equal level). In that case the voice can be significantly reduced by subtracting the right channel from the left channel (referred to herein as the “left minus right” technique), resulting in a mono recording from which the voice is nearly absent. Using this approach, a faint reverberated version of the voice typically is left in the difference signal because stereo reverberation is usually added after the mix. There are several drawbacks to this technique. First, the output signal is always monophonic. In other words it is not possible using this technique to recover a stereo signal from which the voice has been removed. Second, more often than not, other instruments are also panned in the center (bass guitar, bass drum, horns and so on), and the left minus right technique will also remove them, which is undesirable.
U.S. Pat. No. 6,405,163 (the '163 Patent), incorporated by reference above, describes another method which comprises applying a gain to the left and right channels in the short time frequency domain to attenuate center-panned signals. The frequency domain processing method improves on the left minus right technique in that it outputs a stereo signal. While the techniques described in the '163 Patent provide better results than the left minus right approach, the techniques taught by the '163 Patent may result in center-panned signals other than the voice being removed. For example, as noted above percussion, bass, and other instruments are sometimes panned to the center. The '163 Patent teaches restricting the attenuation to voice frequencies in an effort to avoid removing non-voice components. However, the voice spectrum overlaps with the frequency spectra of many instruments that might also be center panned (for example, guitars and snare drums), and components associated with such instruments may also be removed under the approaches taught in the '163 Patent. Therefore, there is a need for a way to remove a center-panned voice component without also removing components associated with other center-panned signals, including signals in the voice frequency range.